This invention pertains to a process and apparatus for the production of a positive electrode in the form of a ribbon, for primary and secondary cells, and more particularly, to the production of a positive electrode formed by rolling a dry powder mixture of an electrochemically active material and a binder onto a metal net or metal mesh, which serves as the current collector.
Such positive electrodes find particular utility in wound batteries with liquid electrolytes based on systems with Li electrodes or H.sub.2 electrodes as the negative (counter) electrode, extending to both nonaqueous and aqueous systems. In such cases, the counter-electrodes are often rolled helically, together with the positive electrode and an interleaved separator.
Such winding requires, above all, high flexibility of the ribbon-like or foil-like electrode materials. The usual practice is to wind such electrodes in a wet process, e.g., by painting both sides of a perforated metal web with a metal oxide paste, as disclosed in DE-OS 2 903 074. In practice, production of the wound electrode body commences with preparation of the paste, and the maintenance of a suitable viscosity, and ends with a careful drying process in which the formation of cracks in the adhering mass layers must be avoided. Such processing requires considerable technical effort.
DE-PS 1 496 289 discloses a dry process in which the powdered active material is continuously forced between forming rolls, into the lattice of a metal mesh (the carrier net). In such case, the interstices of the mesh are filled in the zone of compression developed between the rolls, from one side. However, this disclosure gives only an approximate reference to the final thickness of the resulting electrode ribbon, stating that the carrier net has an initial thickness of 0.5 to 2.5 mm and is compressed (by rolling) to preferably 25% of its original thickness.